A conventional ion source includes an extraction plate having one extraction aperture. Ions are extracted from the extraction aperture into a well defined ion beam. The extraction aperture may have a slit shape to extract an elongated ion beam generally referred to as a ribbon beam. The extraction aperture may have a circular shape to extract a generally circular shaped ion beam generally referred to as a spot beam. Many ion implant applications treat an entirety of a front surface of a workpiece with the ion beam where photoresist defines areas of the workpiece to be treated. In other ion implant applications not using photoresist, it is desirable to form a two dimensional pattern on the workpiece. In one example, the workpiece may be a solar cell such as a selective emitter solar cell where it is desirable to form an interlaced pattern of doped regions. These doped regions are located underneath contacts on the completed selective emitter solar cell to lessen contact resistance and hence improve the overall efficiency of the selective emitter solar cell (the percentage of light converted to electrical energy).
To create a two dimensional pattern, a plurality of ion sources where each has a single aperture may be positioned in assembly line so a workpiece may be scanned past each ion source in succession. In one example, three separate ion sources each having a different extraction apertures are necessary. The workpiece is scanned past the first ion source to create one particular doped pattern, then scanned past the second ion source to create another doped pattern, and then finally scanned past the third ion source to create yet another doped pattern which together created a desired two dimensional pattern. One drawback with this conventional arrangement is that it requires multiple ion sources and the accompanying expense and maintenance of each ion source. Another drawback is that it takes up additional space in an assembly area which has a premium on floor space.
Accordingly, there is a need in the art for an ion source and ion implanter that overcomes the above-described inadequacies and shortcomings.